The present invention pertains to the mechanical connector art and, more particularly, to a backlash free, continued relative rotation shear joint.
Numerous shear pin joints have been developed in the prior art. Such joints are used in applications wherein a drive source is to be connected to a variable load. If the load exceeds a predetermined value, it is desirable to disconnect the source from the load to prevent damage to the source, the linkage or the load itself.
A particularly critical application of a shear joint is found in the commercial aviation art. Here, various control surfaces of the aircraft such as ailerons and elevators are driven by powered actuators which are controlled via linkage systems, either by the aircraft's avionics or by the pilot. If a critical component fails or a linkage becomes jammed, it is imperative that the failed component or frozen linkage be sheared out of the system thereby permitting continued, alternate control of the actuator. A further advantage of such joints is that if a shear joint is located strategically in a system, the downstream linkage need be designed only for the shear out load value, thereby minimizing both structure and weight.
It is crucial in such avionic controlled flight systems that there be absolutely no backlash between the control input and the powered actuator. Avionic systems often respond to backlash by oscillations, or electronic "hunting" which can result in less system stability than is desirable.
Further, it is important that once the shearing action has occurred there cannot be an unintended reseizing of the control linkage to the frozen element. This reseizing or resultant galling might happen, for example, due to rough edges of the sheared pin rubbing against adjacent surfaces as system operation continues. With such reseizure, it might become impossible for the pilot, through his control, to manually operate the system.
In addition, it is desirable that the mechanism, after shearing has occurred, remain substantially intact and allow relative motion of the input and output mechanisms whereby the unit is easy to repair and there is no chance of portions of the linkage separating and becoming jammed or creating a jam, in other, adjacent equipment.